Saturday, March 16, 2013

Life of a Primrose, Part 7: The Golden Crown (end)

These lessons are adapted from "The Life of a Primrose" inFairy-Land of Science, by Arabella B. Buckley. You might start today by reviewing the parts of a flower, e.g. stigma, stamens. There will be a general review at the end of the lesson.

But why should the primroses have such golden crowns? Plain green ones would protect the seed quite as well. Ah! now we come to a secret well worth knowing.

Look at the two primrose flowers, 1 and 2, and tell me how you think the dust (pollen) gets on to the top of the sticky knob or stigma.

No. 2 seems easy enough to explain, for it looks as if the pollen could fall down easily from the stamens on to the knob, but it cannot fall up, as it would have to do in No. 1.

Now the curious truth is, as Mr. Darwin has shown, that neither of these flowers can get the dust easily for themselves, but of the two No. 1 has the least difficulty.

Look at a withered primrose, and see how it holds its head down, and after a little while the yellow crown falls off. It is just about as it is falling that the anthers or bags of the stamens burst open, and then, in No. 1, they are dragged over the knob and some of the grains stick there. But in the other form of primrose, No. 2, when the flower falls off, the stamens do not come near the knob, so it has no chance of getting any pollen; and while the primrose is upright the tube is so narrow that the dust does not easily fall.

But, as I have said, neither kind gets it very easily, nor is it good for them if they do. The seeds are much stronger and better if the dust or pollen of one flower is carried away and left on the knob or stigma of another flower; and the only way this can be done is by insects flying from one flower to another and carrying the dust on their legs and bodies.

If you suck the end of the tube of the primrose flower you will find it tastes sweet, because a drop of honey has been lying there. When the insects go in to get this honey, they brush themselves against the yellow dust-bags, and some of the dust sticks to them, and then when they go to the next flower they rub it off on to its sticky knob. Look at No. 1 and No. 2 and you will see at once that if an insect goes into No. 1 and the pollen sticks to him, when he goes into No. 2 just that part of his body on which the pollen is will touch the knob; and so the flowers become what we call "crossed," that is, the pollen-dust of the one feeds the ovule of the other. And just the same thing will happen if he flies from No. 2 to No. 1. There the dust will be just in the position to touch the knob which sticks out of the flower.

Therefore, we can see clearly that it is good for the primrose that bees and other insects should come to it, and anything it can do to entice them will be useful.

Now, do you not think that when an insect once knew that the pale-yellow crown showed where honey was to be found, he would soon spy these crowns out as he flew along? or if they were behind a hedge, and he could not see them, would not the sweet scent tell him where to come and look for them? And so we see that the pretty sweet-scented corolla is not only delightful for us to look at and to smell, but it is really very useful in helping the primrose to make strong healthy seeds out of which the young plants are to grow next year.

At this point we might have gone further, and studied how the fibres and all the different vessels of the plant are formed, and a wondrous history it would have been. But it was too long for one hour's lecture (or seven natural-history lessons), and you must read it for yourselves in books on botany.

We had to pass on to the flower, and learn the use of the covering leaves, the gaily colored crown attracting the insects, the dust-bags holding the pollen, the little ovules each with the germ of a new plantlet, lying hidden in the seed-vessel, waiting for the pollen-grains to grow down to them. Lastly, when the pollen crept in at the tiny opening we learned that the ovule had now all it wanted to grow into a perfect seed.

And so we came back to a primrose seed, the point from which we started; and we have a history of our primrose from its birth to the day when its leaves and flowers wither away and it dies down for the winter.

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